[Mathieu Trudel-Lapierre <mathieu.tl@gmail.com>]

I've been playing with fixing Ubuntu bug 1097570; trying to debug a script we
use for the EFI images which detects where to boot from based on the location
of a .disk/info file.

Turns out this mostly works, except for the fact that grub appears to always
list devices in a specific order, which interferes with the detection if more
than one device contains that file.

I think I can make this work appropriately provided we:
  - Use hints for search --file;
  - Have some value to pass to --hint= designating the boot drive.

Included is a patch that adds a "bootdrive" variable alongside cmdpath; which
contains just the drive designation for the boot device, to be used as such:

search --set=root --hint=$bootdrive --file .disk/info

I'd much appreciate review on that patch :)